Phosphatidylcholine Cation—Tyrosine π Complexes: Motifs for Membrane Binding by a Bacterial Phospholipase C

Abstract

Phosphatidylinositol-specific phospholipase C (PI-PLC) enzymes are a virulence factor in many Gram-positive organisms. The specific activity of the Bacillus thuringiensis PI-PLC is significantly increased by adding phosphatidylcholine (PC) to vesicles composed of the substrate phosphatidylinositol, in part because the inclusion of PC reduces the apparent Kd for the vesicle binding by as much as 1000-fold when comparing PC-rich vesicles to PI vesicles. This review summarizes (i) the experimental work that localized a site on BtPI-PLC where PC is bound as a PC choline cation—Tyr-π complex and (ii) the computational work (including all-atom molecular dynamics simulations) that refined the original complex and found a second persistent PC cation—Tyr-π complex. Both complexes are critical for vesicle binding. These results have led to a model for PC functioning as an allosteric effector of the enzyme by altering the protein dynamics and stabilizing an ‘open’ active site conformation.

Alchemical Free Energy Calculations on Membrane-Associated Proteins

“…The results indicated that one full lipid in the pore exhibits an unfavorable binding free energy (+41.8 ± 3.3 kJ/mol). In recent studies by Waheed et al, the free energy cost of alanine substitution of aromatic residues in peripheral membrane proteins 174 and phosphatidylinositol-specific phospholipase C (PI-PLC) enzymes 175 was computed. This was performed to examine the contribution of the cation-π interactions of the aromatic residues with choline-containing lipids in peripheral membrane protein affinity.…”